1. Field of the Invention
The present invention relates generally to a rotating magnetic storage disk drive and, more particularly, to a disk drive having a mass balanced load beam assembly which forms part of a head gimbal assembly ("HGA") in a head stack assembly ("HSA") in such a disk drive and reduces the possibility of "head slap" due to mechanical shock.
2. Description of Related Art
A conventional disk drive has a head disk assembly including at least one magnetic disk ("disk"), a spindle motor for rapidly rotating the disk, and a Head Stack Assembly ("HSA") that includes a transducer head carried by a slider (collectively a "head") for reading and writing data. The head stack assembly is controllably positioned by a servo system in order to read or write information on the disk. The typical head stack assembly has two primary portions: (1) an actuator assembly that moves in response to the servo control system and (2) a head gimbal assembly ("HGA") that extends from the actuator assembly and biases the head towards the disk.
The industry presently prefers a "rotary" actuator assembly including an actuator body that rotates on a pivot assembly, a coil that extends from one side of the actuator body to interact with a pair of permanent magnets to form a voice coil motor for moving the actuator body, and an actuator arm that extends from an opposite side of the actuator body to support the head gimbal assembly.
The conventional HGA includes a suspension assembly, an electrical interconnect means such as wires, and a head. The suspension assembly itself comprises a base plate, a load beam and a gimbal. The base plate rigidly connects a base portion of the load beam to the actuator arm. The load beam has a hinge end that pivotally connects to the actuator arm and a gimbal end that connects to the gimbal which carries the head. The load beam transmits a biasing force known as a gram load to the head to "load" it against the disk.
A rapidly spinning disk develops a laminar air flow above its surface which, because of the characteristics of the slider, lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be "flying" over the disk when in this state. The load beam assembly has a spring function which provides the gram load biasing force or "pre-load," and a hinge function which defines a pivot axis and permits the head, supported by the gimbal, to follow the surface contour of the spinning disk.
The conventional HGA is unbalanced in that most of its mass is located distal to the pivot axis. Disk drives using conventional HGAs have long been plagued by product failure due to "head slap," the phenomenon that occurs when the acceleration due to mechanical shock to the drive acts on the unbalanced mass of the HGA, exceeds the pre-load, and causes the head to separate from and subsequently impact the disk surface. This impact between the disk and the sharp corners of the slider can damage the disk, corrupt the data stored in that area, and even cause catastrophic tribological failure.
Head slap can occur during the disk drive manufacturing process, during transport, during assembly into computer systems, or during the use of those systems. Head slap can also occur in some drives in which a "tang" extending from the actuator coil slams into a limiting mechanism or "crash stop" during normal power down operation.
In addition, disk drives designed for the mobile computing market must be able to withstand the abuse imparted to portable computers. This is especially important for drives designed to be removable storage devices. Removable drives can easily be subjected to significant shock G forces even when dropped only a few inches onto a hard surface.
Prior efforts to reduce the head slap problem have included trying to keep the head from leaving the disk surface by increasing the G level threshold needed to cause separation and trying to minimize the damage after separation occurs. Typical efforts have included:
Decreasing the effective mass of the suspension and slider by decreasing suspension length, width, material thickness, material composition, etc.; PA1 Increasing the pre-load biasing force; PA1 Moving the center of mass toward the hinge by narrowing the load beam assembly as it approaches the slider; PA1 Increasing the robustness of the disk surface by using glass substrates, hydrogenated carbon or other tough overcoats, or both; PA1 Radiusing the corners and edges of the air bearing surface and sides of the slider that may contact the surface of the disk; and PA1 Adding stops that limit the separation between the slider and disk to reduce the impact force without reducing the ease with which the slider leaves the disk in the first place.
While these are improvements, an examination of industry literature and quality reports indicates that head slap is still the number one cause of HDA failure in the field. There is a significant need, therefore, for a head gimbal assembly in a disk drive that further reduces the likelihood of head slap.